It known that cathode ray imaging tubes manufactured in typically-automated assembly processes exhibit tube-to-tube differences in the focus and/or other electron beam-related aspects or characteristics of screen-carried images generated during normal operation of the tube. These differences typically result from variations in manufacturing and/or component tolerances, orientations, alignments and like factors, the results of which generally become apparent only after assembly of the tube and sealing of its envelope have been completed and the tube tested to examine its operation. Because of the difficulty of minimizing such variations, and the virtual impossibility of eliminating them, during manufacture while economically producing a competitively-priceable product, efforts are made to "fine-tune" each tube after its assembly and sealing. Most comonly, the electrostatic field-effected focusing of the electron beam is adjusted by operating the tube to observe deficiencies or misalignments of the beam on the screen, following which small permanent magnets or the like are selectively secured about the exterior of the tube neck to distort the electrostatic focusing field and, thereby, the effect of the field on the imaging beam. This procedure, although somewhat effective, has a variety of drawbacks including its labor intensive and relatively inexact nature and the substantial possibility that the magnets may at some point during the life of the tube work themselves loose or otherwise shift in position, distorting the focusing field in unanticipated and unintended ways. This procedure is also relatively inflexible and cannot be readily applied to correct or affect other imaging or image-affecting characteristics of the electron beam not directly associated with the operation of the focusing device.